1. Field of the Invention
The present invention relates to hand held printers, and, more particularly, to a hand held printer with color misalignment correction.
2. Description of the Related Art
A hand held printer, also sometimes referred to as a hand-operated printer, is a printer that mounts a printhead and ink supply, which may be in the form of an ink jet printhead cartridge, wherein the printer itself is moved relative to the print medium, such as a sheet of paper, to position the printhead relative to the print medium. Thus, unlike a typical desktop printer, the hand held printer does not include a drive mechanism for physically positioning the printhead relative to the print medium, nor does a hand held printer include a media feed system for feeding a sheet of print media.
In a hand held printer, an optical encoder or another location-sensing device is used to provide position data for firing the printhead by sensing the relative motion of the hand held printer relative to the print medium. Thus, such a hand held printer is designed to print a single swath having a height corresponding to the height of the printhead. However, when using a hand held printer, there is a tendency to sweep the printer in a slightly curved arc rather than in a straight line.
In color printing, the different color nozzles are lined up in vertical columns. As one example, in the case of three colors, the three columns of nozzles may eject yellow, magenta, and cyan inks from the first, second, and third columns, respectively.
FIG. 1 illustrates one problem associated with attempting to print color using a hand held printer. FIG. 1 illustrates printing as a result of using a hand held printer having a color printhead 100 including a yellow column of nozzles 100-1, magenta column of nozzles 100-2, and cyan column of nozzles 100-3, and while trying to print a composite gray color 102, for example, with the color printhead 100 rotated or not perpendicular to the motion path 103. In this case, the color printhead 100 leaves a yellow line 104 and a red line 106 (composite yellow and magenta) at the top of each swath, and a blue line 108 (composite magenta and cyan) and a cyan line 110 at the bottom of each swath. The height of the lines corresponds to the tilt of color printhead 100. For example, a 45 degrees tilt of color printhead 100 with a two millimeter horizontal separation between the yellow column of nozzles 100-1 and the cyan column of nozzles 100-3 will cause a two millimeter vertical offset between the yellow column of nozzles 100-1 and the cyan column of nozzles 100-3.
Also, as illustrated in FIG. 2, while trying to print the composite gray color 102, for example, due the horizontal spacing of the yellow column of nozzles 100-1, magenta column of nozzles 100-2, and cyan column of nozzles 100-3, an abrupt stopping of the hand held printer 10 during the printing of a print swath may result in distinct vertical bands at the end of the swath. In the present example, the swath ends with a blue vertical band 112 (composite magenta and cyan) and a cyan vertical band 114 at the end of the swath.
What is needed in the art is a method for correcting misalignment between the different columns of color nozzles during color printing with a hand held printer.